In a historic ritual steeped in medieval pageantry, the conclave of cardinals convenes at the Vatican today to select a new pope.

The veiled and secretive election was set to begin with 115 red-robed cardinals filing into the Sistine Chapel, where they will deliberate in the utmost secrecy. Jamming devices have been installed to foil eavesdropping equipment.

The cardinals arrived at the gates of Vatican City yesterday in a steady rain.

Their cars passed over the gray cobblestones to the Domus Sanctae Marthae hotel, where they are staying when the day’s deliberations are over. Pope John Paul II built the $20 million hotel to replace the Spartan quarters of past conclaves.

The rules of the conclave are strict: Cellphones, newspapers and television are verboten.

All staff – including drivers, who will shuttle the cardinals the few hundred yards from the hotel to the Sistine Chapel – have taken vows of silence. Anyone who leaks information risks automatic excommunication.

Catholics should have a new pope by Friday.

The election has not lasted longer than five days in the past century. The 1978 conclave that chose John Paul II took eight ballots over three days.

Picking a pope requires a two-thirds majority of the 115 cardinals. Among Vatican watchers and Internet betting sites, the top candidate is conservative Joseph Cardinal Ratzinger, 78, of Germany.

Before going to the Vatican, some cardinals held public Masses around the Eternal City.

“The new pope has already been chosen by the Lord. We just have to pray to understand who he is,” Ennio Cardinal Antonelli of Florence said at one of the services.

Electing a pope has at times been a contentious and hard-fought affair, bogged down by political infighting and bids by outside forces to wrest control of the Church. It took nearly three years to choose Gregory X in 1271.

The practice of sequestering cardinals – conclave is Latin for “with a key” – dates back to 1241, when squabbling Church leaders could not reach a decision after 60 days and a Roman senator locked them in a malodorous palace to speed their decision along.

But picking John Paul’s successor is not expected to be so fraught with infighting. All but three of the voting cardinals were installed by John Paul himself, resulting in a largely unified Church.

To begin, the cardinals take an elaborate vow of secrecy and the master of ceremonies shouts, “Extra omnes,” or “Everybody out!”

In voting, each cardinal writes his choice on a card inscribed with the words “I elect as supreme pontiff” and places the ballot in a chalice while kneeling in front of an altar.

The first vote is largely symbolic, with cardinals casting their ballots for friends and respected colleagues who stand little chance of being elected.

Traditionally, the real voting doesn’t begin until the second day.

It’s on the second day when it will become apparent to the cardinals whether there is any sort of consensus or an impasse, experts said.

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Inside the Papal Conclave

An extremely secret vote:

The 115 eligible voters from the College of Cardinals who are in Rome are cloistered within the Sistine Chapel until they elect a successor to Pope John Paul II.

They cannot have any contact with the outside world until the voting is done. All the chapel’s windows are sealed and whitewashed. All entrances to the Vatican are blockaded.

* A new pope is selected when the vote reaches a two-thirds majority.

* If a consensus cannot be reached after three days, the cardinals break for a day of prayer and informal discussion.

* If a decision is not reached after seven more votes, the cardinals can choose to go with a simple majority, or narrow the field to the top two choices.

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THE SISTINE CHAPEL

The Sistine Chapel was completed in 1483 during the reign of Pope Sixtus IV. Its ceiling and walls are adorned by the masterworks of Michelangelo and other artists such as Boticelli.

The chapel is 40.93 meters long and 13.41 meters high, the exact measurements of the Temple of Solomon according to the Old Testament.

A 20-year renovation of the chapel was completed in 1999.

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THE VATICAN GARDENS

The cardinals are able to stroll within the Vatican Gardens during the conclave as long as they keep to themselves and do not divulge anything to outsiders.

The gardens date back to medieval times when vineyards and orchards extended north of the Apostolic Palace. In 1279, Pope Nicholas II had the garden enclosed with walls.

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THE SANTA MARTA RESIDENCE

The $20 million hotel for visiting cardinals and church officials is where the cardinals are sleeping during the conclave.

Completed in 1996, the rooms are spartan, although a vast improvement over the cramped conditions cardinals endured for past conclaves, when they slept on foldout cots, with no air-conditioning or heat, and shared just six bathrooms.